Double snap action switch



Jan. 3, 1956 v F. J. BROCH ,7

DOUBLE SNAP ACTION SWITCH Filed Oct. 21, 1950 4 Sheets-Sheet 1 gg K fa61w 15L.

Jan. 3, 1956 F. J. BROCH DOUBLE SNAP ACTION SWITCH 4 Sheets-Sheet 2Filed Oct. 21, 1950 frzvenia 7 1:20? Jfiroa/Tv/ wwnyw Jan. 3, 1956 F. J.BROCH 2,729,714

DOUBLE SNAP ACTION SWITCH Filed Oct. 21, 1950 4 Sheets-Sheet 4 UnitedStates Patent DOUBLE SNAP ACTION SWITCH Frederick J. Broch, Cambridge,Mass.

Application October 21, 1950, Serial No. 191,447

13 Claims. (Cl. 200-67) This invention relates to snap action mechanismssuch as are used to actuate electrical contacts, valves, and othersimilar off and on devices.

When such devices are operated by the usual single snap actionmechanism, the contacts or valves are subject to arcing or chattering asthe mechanism passes through its dead center position unless friction isintroduced to delay the operation until sufiicient energy or force isbuilt up to insure a rapid transfer through the dead center position. Asthe friction varies with aging, corrosion, and change in elasticity, thereliability of such mechanisms is uncertain particularly when operatedby a slow moving actuator such as a pressure bellows or temperatureresponsive bimetallic strip.

It is accordingly the principal objects of this invention to provide asnap action mechanism which will actuate an associated device, whichwill operate positively at any actuating rate, which is not aiiected byvibration, which requires a small actuating force, which operatesequally well in both directions, which is light in weight, which issmall in size, and which advances the art generally.

A snap switch according to the invention comprises a contact carryingarm pivotally or otherwise operatively attached to a supporting base sothat the movable contact carried by the arm selectively makes with oneor more stationary contacts carried by the base. Two members, preferablyflexible, are interconnected at their free ends, either integrally or bymeans of a hinged or pivoted joint, the opposite ends of the membersbeing operatively attached, for example by a suitable movable joint, topoints upon the contact carrying arm and base respectively thereby toform a snap action. The points of attachment are relatively located sothat the force exerted either by a separate spring or because of theinherent resiliency of the members stresses the members in tension andcompression respectively in one state of equilibrium of the snap action.The resulting movement upon the contact carrying arm normally maintainsthe movable contact in a fixed relation with respect to the stationarycontacts during such state of equilibrium. An actuator is provided forrelatively moving the members so that the eifective line of action ofthe member under tension coincides with the effective line of action ofthe member under compression thereby causing the snap action to passthrough its dead center point with an abrupt snap movement of theinterconnected ends of the members. The point of attachment of the endof the corresponding member to the contact carrying arm is relativelypositioned to reverse the movement upon the arm thereby to transfer themovable contact.

These and other objects, aspects and features will be apparent from thefollowing description of an illustrative specific embodiment of theinvention referring to drawings in which Fig. 1 is a schematic diagramof a double snap action movement incorporating a compression'spring;

Fig. 1a is a schematic diagram of a modification of the movement in Fig.1;

Fig. 2 is a schematic diagram of a second type of double snap actionmovement incorporating a tension spring;

Fig. 3 is a view in partial section of a mechanism incorporating thesnap action movement shown in Fig. 2;

Fig. 4 is a sectional view on line 4-4 of Fig. 3;

Fig. 5 is a schematic diagram of a third type of double snap actionmovement incorporating a leaf spring showing the positions assumed bythe various elements as the movement is actuated;

Fig. 6 is a view similar to that shown in Fig. 5 showing the positionsassumed by the various elements as the movement is returned;

Fig. 7 is a plan view of an embodiment of a double snap actionelectrical switch incorporating the movement illustrated in Figs. 5 and6;

Fig. 8 is an elevation view in partial section of the switch shown inFig. 7;

Fig. 9 is a plan view of another embodiment of a double snap actionswitch having a counterweighted contact carrying arm;

Fig. 10 is an elevation view in partial section of the switch shown inFig. 9;

Fig. ll is a plan view of a further embodiment of a double snap actionswitch incorporating a tension spring; and

Fig. 12 is an elevation view in partial section of the switch shown inFig. 11.

The first embodiment of the invention chosen for the purpose ofdiagrammatic illustration comprises an arm 1 which is pivoted at one endat point 0 as is shown in Fig. 1, the opposite end being biased againsta stop S1 by means of an elastic member such as the helical compressionspring 3 hingedly connected at P to the free or lower end of arm 1. Thearm 1 and the spring 3 comprise the elements of a primary snap actionmovement which is tripped by means of an actuator which exerts a forcerepresented by the arrow F. The actuator F may be any one of the wellknown suitable devices operated mechanically, electrically, thermally,hydraulically or otherwise for applying a component of a force to thearm 1 which results in a turning movement about the pivot point 0 sothat the common connecting point P between the arm 1 and the spring 3follows an arcuate path of travel A. As the point P moves along the pathA, the spring 3 is compressed until the point P1 is reached, theactuator F supplying the energy required for this compression. The pointP1 lies in the line C passing through the arm pivot point 0 and a pointR at the lower end of the spring 3 which bears against a stop C1. Theline of action of the spring 3 coincides with a line C extending fromthe point P1 to the pivot point 0, this being the critical or deadcenter position of the primary movement. When the actuator F moves thearm 1 a differential distance beyond the line C, a component of thespring force is developed tangent to the path A so that the arm 1 isrotated about point 0 by the spring force component until the point Phas moved along the remainder of the path A until it reaches the fixedstop S2 and comes to rest at P2. As the energy for completing themovement of the arm 1 beyond the line C is obtained from the expansionof the spring 3 rather than from the actuator F, such movement is tripfree.

During its trip free travel the arm 1 of the primary movement trips asecondary movement comprising an arm 2 (one end of which is pivoted atO), and the spring 3 which is common to both movements, the spring andthe free or upper end of arm 2 being hingedly connected at the point Rwhich moves along an arcuate path A' about the center The tripping ofthe second movement occurs when the free lower end of the arm 1 reachesthe point P3 which is a head center position of the secondary movementwhere the line of action of the spring 3 coincides with the axis 0 ofthe arm 2 so that a differential move ment of the free lower end of arm1 beyond P3 results in a spring force component tangent to the path ofthe point R which transfers the free upper end of arm 2 to the position2 against the stop C2. The return action is symmetrical, the same or adifferent actuator applying force F to move the arm 1 in acounterclockwise direction until the end i again rests against the stopSi, the primary movement passing with a trip free movement through asecond dead center position (not illustrated} located upon the oppositeside of the center line T from its above mentioned first dead centerposition, the movement being tripped during such trip free movement in amanner analogous to that described in detail above.

A modification of the above-described embodiment is shown in Fig. lawherein the pivot points 0 and O are both located upon the same side ofthe spring 3 rather than upon opposite sides thereof as is the case ofthe first embodiment illustrated in Fig. 1.

In the second embodiment of the invention shown in Fig. 2, a tensionspring 3a is the elastic member employed to interconnect the respectiveends of the arms in and 2:; whose opposite ends are pivotally attachedat the points 0a and 6's respectively. The travel of the end Pa of thearm 1a at which the spring 3a is connected, is limited by stops Sid andS211. 2, connected to the opposite end of the spring 3a, is limited bythe stops Clo and C201. The device is tripped by means of a component offorce Fa, exerted by an actuator (not shown), to move the point he alongthe arcuate path Art to the dead center position Pla of the primarymovement where the line of action of the spring 3:: and the axis of thearm 1a coincide, the energy for the remaining travel of the arm in tothe stop 32a being supplied by the spring so that the travel is tripfree.

As the arm end Pa passes beyond the point F351, at the dead centerposition of the secondary movement where the line of action of thespring 3a coincides with the axis of the arm 2a, the spring force has acomponent tangent to the arcuate path of the arm end Ra which moves thearm 2a. until it rests against the stop C'Z a. The return action of themovement is symmetrical, the primary movement after passing a seconddead center position upon the opposite side of the center line Ta fromits first dead center position, trips the secondary movement in a manneranalogous to that described above.

If the stops C1 and C2 (or Cla or CZa) are made stationary electricalcontacts and the arm 2.- (or 2a) carries a correlated movable contact,it will be evident that the rate of movement or vibration of theactuator will have no effect upon the contacts moved by the secondarymovement which is tripped after the primary movement is in a trip freecondition beyond the control of the actuator thus eliminating theburning and arcing of the contacts encountered in conventional switchesbecause of reduction of contact pressure at the dead center position.

The above-described principle of operation of the movement illustratedin Fig. 2 is utilized in the switch embodiment shown in Figs. 3 and 4-wherein the various analogous elements and positions bear the sameindicia as in Fig. 2. This embodiment comprises a hollow, generallyrectangular base 1 having an open top and two opposed side walls whichare provided with aligned circular recesses or grooves which accommodatecorresponding circular ends of a hollow actuator Fa having the generalshape of a truncated pyramid. A U-shaped member 12 of a conductingmaterial is fastened by its crosspiece to the bottom of the base 10 sothat the legs of the, member extend up into the hollow actuator therebyto provide a support for the pivots 0a and Oa of the arms in and 2a,

The travel of the end Ra of the arm respectively. The arms 1a and 2a areshaped similarly to double cranks with their crankpins deformed as isshown in Fig. 4 to provide seats for securing the respective ends of thespring 3a. The opposite ends of the shaft of the crank arm 1a arejournaled respectively in aligned apertures near the top of the opposedlegs of the member 12, the axis of the shaft forming the pivot point 0a.The ends of the shaft of the crank arm 2a are likewise journaled inaligned apertures in the supporting member 12, the shaft axis formingthe pivot O'a. The ends of the shaft of crank arm 2a are extendedthrough the support legs 12 into the adjacent side walls of the actuatorFa thereby to provide a pivot about which the actuator can be moved.

The above-described switch is tripped by rotating the actuator Fa aboutthe pivot Oa so that the inner wall Sin thereof bears against the crankportion of the arm in to move it beyond the dead center position Plawhereupon the arm moves until it contacts the opposite inner wall S211of the actuator Fa which acts as a stop, such movement being trip freeas described in detail in connection with the embodiment shown in Fig.2. The arm 2a remains against a stop Cia, Which is also an electricalcontact, until the arm in passes through the dead center position Pile:of the secondary movement whereupon the arm 21; moves into contact withits other contact stop C251. The movement of the actuator Pa in theopposite direction returns the arms to their original position, thesequence of operations being similar to that described above withrespect to the first operation of the switch.

in Figs. 5 and 6 is schematically shown a further double snap actionmovement wherein the primary movement comprises a non-rigid link 3 oneend of which is pivotally attached at 36 to a supporting base (notshown) or other relatively stationary point. The opposite end of thelink 3d is joined to one end of a compression spring member whose lineof action is represented by the line 26, the common end point of thelink and spring being designated 28. The secondary movement includes asubstantially rigid contact carrying arm 29 which is pivoted at one endat the relatively fixed point 22. The arm 2i) is biased at one limit ofits travel in its normal position shown in full lines against the lowercontact 24 by means of the compression spring member 26 whose oppositeend is pivotally connected at a point 3% upon the contact carrying armZil intermediate its ends.

The upward movement of the joined end 28 at the opposite end of thespring member is limited by a stop 32. The horizontal movement to theleft of the joined end point 23 along the face of the stop 32 is limitedby the non-rigid link 34, one end of which is pivotally connected at therelatively stationary point 36 as described above. As the opposite endof the non-rigid link 34 is attached to the end of the spring member 26at 28, the link is under a tension stress which holds the spring memberin compression. The downward component of the spring force, exerted bythe spring member upon the point 30, acts through a lever arm, equal inlength to the portion of the arm 20 between the points 2230, thereby tobias the end of the arm 25? against the normally closed contact 24 asmentioned above. It will be noted that the contact force between the arm20 and the contact 24 would be increased by raising the position of thestop 32 relatively to the fixed pivotal point 22 thereby to increase thedownward force component.

The switch is operated by means of an actuator 38 which bears against anintermediate point of the link 34. As the link is non-rigid andpivotally secured at point 36, the movement of actuator 38 to theposition 38' deforms the link so that it now has the configurationindicated by the broken line designed 34'. As the overall length of thelink 34 remains constant, the common end point 28 slides horizontally,to the right, along the face of the stop 32 until the point 28' isreached.

As the actuator 38 is depressed further, the sliding horizontal movementof the point 28 and the accompanying increase in compression of thespring member continues until a point 28" corresponding to an actuatorposition 38" is reached. It will be noted that in this position 38", theactuator deforms the link 34 to the position designated 34 where theportion of the link to the left of actuator position 38 coincides withthe line of action 26 of the spring member. or dead center position ofthe primary movement. A subsequent further differential movement of theactuator to a point below the point 38 moves the part of the link 34which is to the left of the point 38" below the line of action of thespring member 26 so that there is nowadownward component of the forceexerted by said spring member at the point 26". This downward forcecomponent is unopposed so that the part of the link 34 which is to theleft of the point 38" pivots about the final point of application of theactuating force and the spring member 26 pivots about the point 30. Inthis connection it will be noted that an are, such as is indicated bythe dotted line 28b having a radius 28"30, equal in length to thecompressed length of the spring member when the actuator is at itslowest point, lies within an arc 28a traced by the pivotal movement ofthe point 28" about the point which represents the lowest position ofthe actuator so that the spring member expands during this movement.This expansion of the spring member supplies energy so that the point28" moves until it reaches 28t against the face of a lower stop 40without further action on the part of the actuator 38.

As the line of action 26 of the spring member passes the line 26d (Fig.which passes through the points 22 and 30 on the arm 20, the torqueexerted on the arm by the spring member is reversed, i. e., this is afirst dead center position of the secondary movement so that a furtherdifferential movement of the line of action 26 of the spring memberpivots the arm about the point 22 to the position designated 20" whereinits contact end rests against a stationary contact 44 and theintermediate pivotal point 30 moves to 30". This movement of the end ofthe spring member to the point 30" shifts the line of action of thespring member so that the component of spring force tangent to the arc28a is increased thus aiding the movement of the joined end of the linkand spring member to the point 281. The movement of the point 30 to 30"also permits the spring member to expand, thus supplying energy foroperation of the secondary movement. The line of action of the springmemher after the above-described movement and expansion assumes theposition designated 26" (Fig. 6). It will be evident from the above thatthe component of the force of the spring member forcing the arm 20against the contact 44 would be increased if the stop 40 were lowered.

The arm 20 is returned by the spring to its normal position wherein itmakes with the contact 24 upon release of the actuator 38, by reason ofthe fact that the pivot point 36 is spaced above the line 22-30. As theforce exerted by the actuator 38 is removed from the link 34, theportion of the link between the actuator and the end 28 straightens out,taking the position designated 341-, so that the common end 28 movesalong the face of the stop 40 from the point 28t to the point 28! whichresults in a decrease in the force exerted against the contact 44.

In the position Mr that portion of the link which lies between theactuator and the end 28 coincides with the line of action of the springmember 26 which is the second dead center position of the primarymovement, but at this time the link is not yet straight but from theactuator to the point 36 is inclined more steeply than to the left ofthe actuator thus holding the spring under abnormal stress. Since theactuator is free to rise, the spring force tends to straighten the link,causing further upward movement of the actuator which results in anupward component of spring force which, being unopposed, moves Thisposition is the first critical 8 the joined end to the point 28" alongthe arc 28c, whose center of curvature is the actuator point 38" untilthe point 28" upon the face of the stop 32 is reached. Dur ing thismovement of the point 28"): along the arc 28c, the spring member expandsby an amount indicated by the distance between this are and an arerepresented by the dotted line 28d which is the locus which would betraced if the end of the spring member were rotated about the point 30"without expanding. This expansion of the spring member provides energyfor moving the common end 28.

As the dead center position 26'd of the secondary movement is reached,the component of the spring force upon the arm 20 is reversed, returningthe arm to its original position in which it makes with the contact 24.The end of the spring member conjointly moves from 30" to 30 and shiftsthe line of action of the spring member so that the component of springforce tangent to the arc 28c is increased, thus aiding the movement ofthe joined end of the link and spring member to the point 28'. Themovement of the point 30" to 30 also permits the spring member toexpand, thus supplying the energy for the operation of the secondarymovement.

In Figs. 7 and 8 is shown a first practical embodiment of a double snapaction switch which operates according to the principles described indetail above in connection with the schematic diagrams shown in Figs. 5and 6. Accordingly the various components of the switch are numbered tocorrespond with the lines and points of the diagrams in Figs. 5 and 6which have generally similar functions. This switch comprises a base 50molded or otherwise formed of a nonconducting material such as asuitable plastic. The lower, normally closed stationary contact 24' iscarried upon the upper end of a conducting insert 24a whose lower end ismolded into the base 50. The lower end of the base has an aperture withinternal threads for engaging a screw 24b for electrically connectingthe contact to the lead (not shown) from an external circuit. The uppercontact 44 is carried upon the lower side of one end of a bridge member44a whose opposite end is secured to the top of an insert 44b by meansof a screw 44c. The bottom of the insert 44b is molded in the base 50and provided with a threaded aperture for a connecting screw similar tothe screw 24b in the insert 24a described above.

A movable contact 200 for selectively making with the stationarycontacts 24 or 44 is carried upon the end of a substantially rigid arm20 of a conducting material such as bronze or magnesium. The oppositeend of the arm 20 is forked and the ends of the resulting tines arenotched to engage respectively circumferential grooves in two pins 22which are secured in inserts 22a molded in the opposite end of the boss20 from the end at which the contacts are mounted so that the pins forma pivot about which the arm moves to make with the stationary contacts.One or both of the inserts 22a are provided with an internally threadedaperture to receive a screw 22b for connecting to the lead (not shown)of an external circuit.

Re-enforcing strip 20a is welded or otherwise fastened to the bottom ofthe respective tines of the arm 20 thereby to form two steps 30 againstwhich bear the ends of the compression spring members 26. The oppositeends of the spring members 26 are formed integrally with one end of link34 as at the common joined end 28. The opposite end of the link 34' hasan aperture which engages a circumferential groove under the head of ascrew member 36 maintaining the spring members 26 under compression sothat the arm 20 is biased against the lower contact 24. The travel ofthe joined end 28 of the link 34 and the spring members 26 is limited tothe screws 32 and 4% which engage threaded apertures in the base 50.

The switch is tripped by the conical shaped end of an actuator 38 whoseshaft is guided in an aperture in a cover 55 for the base 50. The apexof the actuator 38 depresses the link 34 until the axis thereofcoincides with the line of action of the spring members 26 at the firstdead center position of the primary movement whereupon the joined end 28travels the remaining distance to the stop 40. As the joined end 28passes through the first dead center of the secondary movement, thecontacts transfer so that the movable contact 20c makes with thenormally open stationary contact 44. Upon the releasing of the actuator38, until it returns to a second dead center position of the primarymovement where the axis of the link 34 coincides with the line of actionof the spring members 26, the joined end 28 returns so that it again isin contact with the under side of the head of the screw 32. During thereturn travel of the joined end 28, the line of action of the springmembers 26 passes through the second dead center of the secondary memberso that the arm 20 returns the contact 200 to the normal positionagainst contact 24.

The switch shown in Figs. 9 and is generally similar and operates uponthe same principles as the switch described in detail immediately abovewith the exception of its counterweighted contact arm 120 which isrigidly formed from one piece of metal. The arm 120 is provided with twoknife edges 122a which engage corresponding V-notches in ears 122 whichare bent up from a supporting plate 1232b. The plate 12212 is secured tothe base by means of a flat headed screw 1220 of relatively greatdiameter which is provided with a threaded axial hole for a screw 122dfor connecting a lead (not shown) from an external circuit to energizethe movable contact 200 carried upon the end of the arm. The oppositeend of the arm 12%) is extended beyond the knife edges 122a to supporttwo counterweights 122e and 122 made, for example, of lead so that thearm is statically balanced about its pivot points. The weights 122a and122 are fastened to the end of the arm 129 by means of two screws 122g,the base 150 and cover 155 being modified so that they do not interferetherewith. The remaining switch elements are similar in construction andbear the same indicia as the corresponding elements in the embodiment ofthe switch shown in Figs. 7 and 8 and described in detail heretofore.

A further embodiment of the invention, wherein the compression springmembers 26 are replaced by two rigid members 126 and the compressionstress is introduced by means of a helically wound tension spring 134,is shown in Figs. 11 and 12. One end of the spring 134 is securedagainst a knife edge forming one wall of a small aperture in the centerof the joined ends 128 of the members 126. The opposite end of thespring 134 is similarly secured in an aperture near one end of acomparatively rigid link 134a. The opposite end of the link 134a isprovided with a second aperture whose wall engages a circumferentialgroove in a screw 136. The contact carrying arm 20 is generally similarto the arm 26 shown in Figs. 7 and 8 and described heretofore, but isprovided with a greater ofifset and modified pivotal connections 130with the ends of the compression members 126 respectively. The remainingelements are similar in construction and bear similar indicia to thecorresponding elements in the two embodiments described in detail above.

It will be evident that in the normal position of the switch, asindicated by the solid lines in Fig. 12, the tension in the spring 134causes a force to act upon the points 130 of the arm 2i) which is theequivalent to force exerted by the spring members 26 upon points 36 ofthe arms in the previously described embodiments so that the movablecontact 205 is biased against the lower stationary contact 24. As theactuator 38 is depressed, it contacts the link 134a which pivots aboutthe screw 136. As the link 134:: is substantially rigid, the endconnecting with the spring 134 is moved downwardly until the line ofaction of the spring coincides with the axis of the members 126 which isthe first dead center position of the primary movement.

it should be noted that the link 134a acts as a lever so that therequired movement of the actuator 38 is reduced.

Upon reaching the above mentioned dead center position, the primarymovement moves to the position shown in broken lines with the joined end128 resting upon an abutment of the base 50a which acts as a stop. Thedownward movement of the link 134a is arrested by by means of a stopsuch as the screw 140a. During this movement the arm 20 is moved so thatthe contact 200 is transferred to make with the upper stationary contact44 in a manner similar to that which has been described in detail inconnection with previous embodiments.

Upon the release of the actuator 38, the spring 134 moves upwardly untilits line of action coincides with the axis of the members 126 whereuponthe spring and link return to their original position, the arm 20returning during this trip free movement so that the contacts 200 and 24again make.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

I claim:

1. A snap action switch comprising an elongate base, means adjacent toone end of the base for supporting at least one fixed electricalcontact, a substantially rigid contact carrying arm extendinglongitudinally of the base, fixed means adjacent to the opposite end ofthe base defining a horizontal pivotal axis for the contact carryingarm, said arm having a contact adjacent to its free end which isarranged selectively to make with the fixed contact, two elongateelements extending longitudinally of the base, those ends of saidelements which are nearer to the fixed contact being joined together,one of said elongate elements being normally in tension and the other incompression, means anchoring that end of the tensioned element, which isnearer to the pivot means for the contact carrying arm, to the base, thecorresponding end of the compression element engaging the contactcarrying arm at a point intermediate the ends of said arm and normallyexerting force against the contact carrying arm in a direction to keepthe movable contact in engagement with the fixed contact, means forlimiting motion of the joined ends of the tension and compressionelements, and actuating means for applying force to the tension element,at a point nearer to the anchored end of said element than to its otherend, so as to decrease the effective length of the tension element andthereby shift the effective line of action of the tension element untilsaid line of action first coincides with and then passes the normal lineof action of the compression element, thereby causing an abrupt snapmotion of the joined ends of said elements and a shift in the line ofaction of the compression element such that the latter now exerts forceon the contact carrying arm in a direction opposite to the force appliedby the actuating means thereby carrying the movable contact away fromthe fixed contact.

2. A snap action switch according to claim 1, wherein the fixed contactis located wholly to one side of the longitudinal center line of thebase, one end of the contact carrying arm being bifurcated to providespaced parallel legs disposed symmetrically at opposite sides of thelongitudinal center line of the base, each leg terminating at one end ina horizontal knife edge, said edges being aligned and engaging the pivotmeans carried by the base, the free end portion of the contact carryingarm on which the movable contact is mounted being unsymmetrical in planand comprising a portion which overhangs the fixed contact and on whichthe movable contact is mounted.

3. A snap action switch according to claim 2, wherein each leg of thecontact carrying arm has a step spaced from the knife edge, thecompression element having two parallel elongate members joined togetherat one end to one end of the tension element, the latter beinginterposed between said parallel members, the free ends of said parallelmembers of the compression element seating against the steps of thecorresponding legs of the contact carrying arm, and means fixedlyanchoring the other end of the tension element to the base.

4. A snap action switch comprising an elongate base of insulatingmaterial, means near one end of the base supporting vertically spacedupper and lower contacts, a substantially rigid contact carrying armextending longitudinally of the base, means defining a horizontalpivotal axis for one end of said arm adjacent to the other end of thebase, a movable contact mounted on the other end of said arm andinterposed between the stationary contacts, two elongate flexibleelements extending lengthwise of the base, one being in tension and theother in compression, those ends of said elongate flexible elementswhich are nearer to the fixed contacts being joined together, theopposite end of the tensioned element being anchored to the baseadjacent to the fulcrum means for the contact carrying arm, thecorresponding end of the compression element engaging a step carried bythe contact carrying arm at a point intermediate the ends of said armand normally exerting force on said arm in a direction to keep themovable contact engaged with one of said fixed contacts, said arm andflexible elements constituting a snap action mechanism having two statesof equilibrium, actuating means for applying deflecting force to one ofsaid elongate flexible elements thereby to shift the effective line ofaction of the tensioned element until said line first coincides with andthen passes the normal line of action. of the compression elementthereby causing an abrupt snap movement of the joined ends of saidelongate elements and a shift in the line of action of the compressionelement such that the contact carrying arm is moved to engage themovable contact with the other fixed contact, and means for determiningthe contact pressure between the movable and the respective fixedcontacts comprising two independently adjustable stops.

5. A snap actionswitch of the kind wherein an elongate rigid insulatingbase is provided near one end with means supporting upper and lowervertically spaced fixed contacts, a movable contact engageablealternatively with the respective fixed contacts, and a rigid lever ofconducting material on one end of which the movable contact is mounted,means carried by the base adjacent to the opposite end of the base andwhich defines a fixed horizontal pivotal axis for the opposite end ofthe contact carrying lever, an elongate tension element, a portion atleast of whose length is flexible, means anchoring one end of saidtension element to the base adjacent to said pivotal axis, a compressionspring element joined at one end to the other end of the tensionelement, means limiting motion of the joined ends of said elementsupwardly and downwardly, the opposite end of the compression springelement seating against a step carried by said lever at a pointintermediate the ends of the latter, the step facing toward that end ofthe base at which the fixed contacts are located, the parts being soarranged that the compres sion spring element normally exerts acomponent of force such as to urge the movable contact toward the lowerfixed contact, a movable actuator which engages the tension element at apoint intermediate the anchored end of the latter and the point wherethe tension and compression spring elements are joined, saidactuatorconstituting means whereby downward force may be exerted transversely ofthe tension element to cause portions of the latter to lie in planeswhich intersect to form an obtuse angle Whose apex is directeddownwardly and so positioned relatively to the horizontal plane of saidpivotal axis as to cause a shift in the direction of the force exertedby the compression spring element thereby moving the movable contacttoward the upper fixed contact.

6. A snap action switch according to claim 5, wherein the pivotal axisfor the contact carrying lever is in a horizontal plane which is belowthe lower of the fixed contacts.

7. A snap action switch according to claim 5, wherein the anchored endof the tension element is at a point above the horizontal plane of thepivotal axis for the contact carrying lever.

8. A snap action switch according to claim 5, having means forrelatively varying the vertical distance between the point of anchorageof the tension element to the base and the horizontal plane of thepivotal axis of the contact carrying lever.

9. A snap action switch according to claim 5, further characterized inthat the tension element is transversely flexible throughoutsubstantially its entire length but normally substantially rectilinearfrom its anchorage point to its junction with the compression springelement.

10. A snap action switch according to claim 5, wherein the means forlimiting upward and downward movement of the point at which thecompression and tension elements are joined comprises independentelements disposed at opposite sides of the horizontal plane of thepivotal axis of the contact carrying lever. 1

11. A snap action switch according to claim 5, wherein the means forlimiting motion of the point of junction of the tension and compressionspring elements consists of two screws, having threaded engagement withthe base, the junction point of the tension and compression elementsbeing interposed between the head of one screw and the tip of the otherscrew.

12. A snap action switch according to claim 5, comprising meansoperative statically to balance the contact carrying lever about itspivotal axis.

13. A snap action switch according to claim 5, wherein the contactcarrying lever is provided with a bracket extending to the opposite sideof the pivotal axis, and a counterweight carried by said bracketoperative statically to balance the contact carrying lever about saidaxis.

References Cited in the file of this patent UNITED STATES PATENTS Re.17,646 Johnson Apr. 22, 1930 1,910,510 Warner May 23, 1933 2,144,120Parks Jan. 17, 1939 2,228,523 Johnson Jan. 14, 1941 2,459,661 MacFarlandJan. 18, 1949 2,476,045 Kaminky July 12, 1949 2,508,040 Ransome May 16,1950 2,510,021 Kaminky May 30, 1950 2,566,534 Reger Sept. 4, 19512,589,563 Miller Mar. 18, 1952 FOREIGN PATENTS 965,336 France Sept. 8,1950

